1. Field of the Invention
The present invention relates to a substrate processing apparatus and method to form the coating film on a to-be-processed substrate by applying a chemical solution.
2. Description of the Related Art
In lithography employed for manufacturing a semiconductor device, a semiconductor wafer with a to-be-processed film thereon is coated with a chemical solution such as a resist, which serves as a resist film. Selected portions of the resist film are exposed to light. After that, the resist film is developed to obtain a resist pattern. Using this patterned resist, the to-be-processed film is processed, whereby a desired pattern is formed on the semiconductor wafer.
A chemical solution such as a resist is guided onto a semiconductor wafer via a solution supply line (pipe) and dripped through a discharge nozzle. Depending upon the type of chemical solution, the number of particles of the solution is increased in the pipe. Most of the particles are eliminated by a final filter provided across the solution supply line. However, particles intermittently occur in the solution accumulated between the final filter and discharge nozzle, and the particles occurring at the secondary side of the final filter may well become coating defects.
Further, the supply of the solution is stopped after coating of one wafer and before coating of another wafer. At this time, the solvent in the solution vaporizes at the tip of the nozzle, and particles occur in the resultant condensed solution. This causes defects in coating.
In accordance with the development of pattern microfabrication, multi-layer resist also have come to be used in view of resolution. In a process using a multi-layer resist, a lower resist layer is formed on a to-be-processed film provided on a semiconductor wafer. Subsequently, an intermediate material as a sol-gel liquid, such as SOG, is coated and heated to form an intermediate layer. After that, a resist solution is coated to form an upper resist layer. The coating materials of the intermediate layer and upper resist layer are discharged through a nozzle having a tapered tip (JP-A 2003-112083 [KOKAI]).
However, in the case of coatings made of a sol-gel material for an intermediate layer represented by SOG, coating defects that are considered to result from gel in the solution are liable to occur. The inventors of the present invention have conducted research and found that gel growth occur at the condensed surface, i.e., gas-liquid boundary, of a sol-gel solution at the tip of a solution discharge nozzle.
Thus, when a chemical solution is dripped through a nozzle onto the surface of a to-be-processed substrate, the particles occurring between a final filter and nozzle, and/or the particles occurring at the tip of the nozzle may cause coating defects. Further, in the case of using a chemical solution in a process utilizing a multi-layer resist, gelling easily occurs at the tip of the nozzle and causes coating defects to occur.